HIV-infected individuals on antiretroviral therapy (ART) are at increased risk for cardiovascular disease (CVD), possibly due to inflammation that persists despite aggressive HIV treatment. Patients with rheumatoid arthritis, like those with HIV, have increased CVD risk and high levels of inflammation. Low-dose methotrexate (LDMTX) is a safe treatment for patients with rheumatoid arthritis that appears to reduce CVD risk. The Cardiovascular Inflammation Reduction Trial (CIRT) recently received funding from the NHLBI to enroll 7500 subjects in a randomized clinical trial to evaluate the effects of LDMTX on the secondary prevention of CVD events and mortality among patients with prior CVD and ongoing inflammation. Because the factors that contribute to persistent inflammation in the setting of HIV infection are different thn those in the general population and individuals with HIV infection are excluded from the CIRT, its results will not be generalizable to the growing population of individuals living with HIV in te United States. The NIAID AIDS Clinical Trials Group has agreed to fund the clinical trials network infrastructure and costs for a randomized trial to evaluate the safety and feasibility of a LDMTX intervention in individuals with HIV (study A5314). We are submitting this application to the NHLBI for support of our proposed measures of vascular function and inflammation, since these areas are more in line with the priorities of NHLBI. We propose to evaluate the effects of LDMTX treatment on endothelial function, inflammation, and immune activation in virally suppressed, HIV-infected individuals at increased CVD risk as part of study A5314, so data regarding the effectiveness and safety of LDMTX can be collected simultaneously. This study also will provide mechanistic insights into the effects of LDMTX on CVD risk and will provide a rationale for more extensive studies to evaluate anti-inflammatory interventions on CVD risk in individuals with HIV. It will leverage an existing NIH- funded clinical trials infrastructure to perform this trial at a significantly reduced cost to the NHLBI. Our central hypothesis is that persistent inflammation and immune activation contribute to increased CVD risk in HIV-infected individuals on stable antiretroviral therapy (ART). To investigate this hypothesis, we will perform a randomized, double-blind, placebo-controlled clinical trial to evaluate the effects of LDMTX in virally suppressed, HIV-infected individuals on stable ART. This investigation has three specific aims that assess whether treatment with LDMTX will (i) improve endothelial function, as assessed by flow-mediated vasodilation of the brachial artery; (ii) reduce hsCRP and interleukin-6 levels, inflammatory markers of CVD risk; and (iii) decrease levels of immune activation and senescence. We expect that LDMTX therapy will improve arterial function by lowering inflammation and that this mechanistic, proof-of-concept study will demonstrate the importance of inflammation and immune activation in HIV-associated CVD, thus forming the basis for future interventional studies to identify strategies that reduce CVD risk in individuals with treated HIV infection.